It is known that in-flight refueling, intended to transfer fuel from one aircraft in flight (called the refueling aircraft) to another aircraft in flight (called the refueled aircraft) is a very demanding task, in particular for the pilot or pilots of the refueled aircraft. This task requires precision, speed, and firmness. In particular, the pilot must adjust the position of the refueled aircraft with a precision of the order of 20 cm to be able to engage the in-flight refueling probe in the refueling drogue of the refueling aircraft.
A so-called vertical load factor control law C* (or C*U) is usually employed to control the pitch axis of an aircraft having an electrical flight control system. The main principle of this law C* is to convert a command from the pilot (via the control column) into a high-speed load factor command and into a low-speed load factor and pitch rate command. These commands are converted into deflection instructions for an elevator of the aircraft.
For a law C* of this usual kind, the increase in the lift of the aircraft is caused by an increase in the angle of attack of the aircraft which for its part is caused by the movement (or deflection) of the elevator.
Accordingly, at the start of the command, even if the commanded load factor is positive, the load factor measured at the center of gravity of the aircraft is negative. This phenomenon leads to a delay in the response of the aircraft and thus to a loss of precision and a loss of firmness during certain piloting phases, for example, during in-flight refueling.